Figures...vii Tables... ix Acknowledgments... xi Foreword... xiii Preface...xv

Transcription

1 Contents Figures...vii Tables... ix Acknowledgments.... xi Foreword.... xiii Preface...xv INTRODUCTION 1 1 ASSESSING THE PROBLEM 5 Sources of Iron and Manganese....5 Groundwater Sources...6 Surface Water Sources....7 Health Effects...9 Regulatory Standards SUSTAINABILITY AND ENGINEERING DESIGN 13 An Indefinite Definition...14 Importance of the Sustainable Approach How Is Sustainability Measured?...16 Core Sustainability Factors...20 Sustainable Iron and Manganese Removal...21 Looking Ahead BASIC CHEMISTRY 25 Chemical Symbols, Common Formulae...25 Ionization...26 ph Value...27 Chemical Forms of Iron and Manganese Organic Chemistry...31 iii

2 Iron and Manganese Removal Handbook 4 OVERVIEW OF TREATMENT TECHNOLOGIES 35 Overview of Technologies...37 Sequestration Oxidation, Clarification, Filtration...38 Oxidation, Manganese Dioxide Coated Media Filtration Oxidation, Membrane Filtration...39 Biological Filtration Residuals...40 Evaluation and Selection Criteria for Optimum Treatment Treatment System Design Elements and Work Flow...42 Summary OXIDATION 47 ph Adjustment and Reaction Time...48 Aeration...51 Chlorination Permanganate...56 Chlorine Dioxide (ClO 2 )...60 Ozone...61 Testing Equipment...62 Test Kits...64 Methods of Testing for Soluble Metals...64 Testing Oxidation Efficiency Testing for Chemical Oxidant Demand...68 Summary CLARIFICATION 73 Benefits of Clarification...73 Clarification Fundamentals Sustainability FILTRATION 85 Filtration Selection...85 Manganese Greensand...89 Manganese Dioxide Coated Sand...95 Manganese Dioxide Ore (Pyrolusite)...98 Other Forms of Hybrid Media Biofiltration Ion Exchange iv

3 Membranes Sustainability RESIDUALS 117 Source Water Quality Treatment Processes Local and Regulatory Issues Residuals-Handling Options Sustainability DISTRIBUTION SYSTEM WATER QUALITY 133 Importance of Discolored Water to Operations Scale Formation and Structure Water Quality Factors Implementing Solutions to Address Discolored Water Sustainability CASE STUDIES 149 Case Study No. 1: Springfield Well Field Case Study No. 2: City of Tallahassee Well No Case Study No. 3: Runyon Water Treatment Plant Upgrade Case Study No. 4: United Water Wyandotte WTP GLOSSARY 175 REFERENCES 187 APPENDIX A: PILOT STUDIES 193 APPENDIX B: CALCULATION TOOLS 201 INDEX 207 v

4 Introduction This book is an updated version of the Iron and Manganese Removal Handbook, published by the American Water Works Association in The original handbook was developed in part as a practical training tool for operators and engineers. Over the past two decades, a number of issues have impacted the design and operation of iron and manganese treatment systems: Lower maximum contaminant levels (MCLs) for disinfection by-products Broader understanding of the impact of radionuclides on the performance of treatment systems Limited availability of glauconite greensand Desire to have systems that are sustainable Advancements in membrane technology Need to treat additional synthetic organic compounds and the impact of multiple treatment processes on the iron/manganese removal system Increased attention to distribution system water quality Increased use of oxidants other than traditional chlorine gas and 15 percent sodium hypochlorite The purpose of this handbook is the same as the original handbook, which was developed as a training tool and as a useful reference for anyone interested in removing iron and manganese from potable water, as well as the basic operation of water treatment and filtration plants. In this new edition, more detail is devoted to the selection and design of the treatment process and to minimizing the use of vendor-engineered packages that have become so common throughout the industry. Unit 1

5 2 Iron and Manganese Removal Handbook processes are described and calculations are provided so that the reader can understand the impacts of changes to the design components. This edition also attempts to address the question why. When approaching any water quality issue, the investigator may wish to consider why decisions are made and standards followed. For example, why is the secondary maximum contaminant level (SMCL) at 0.3 mg/l for iron? Why is chlorine the most common oxidant? Why is the traditional filter loading rate 3 gpm/ft 2? In an effort to increase the understanding of water professionals, this book is written with the why question in mind. The handbook is organized into the following chapters: Chapter 1. Assessing the Problem Chapter 1 describes the occurrence of iron and manganese in drinking water systems. It presents an overview of applicable regulations and of the potential simultaneous compliance issues that may be impacted by iron and manganese treatment. Chapter 2. Sustainability and Engineering Design This chapter defines sustainability, examines the importance of the sustainable approach, considers how sustainability can be measured, and outlines core sustainability factors as they apply to the removal of iron and manganese. Chapter 3. Basic Chemistry This chapter explains the basic chemical reactions associated with iron and manganese. These chemical reactions affect the forms in which iron and manganese appear and the types of treatment that can be used to control and remove them. Chapter 4. Overview of Treatment Technologies This chapter provides the framework for the remaining chapters of the book and introduces the reader to the potential treatment options that are available to address iron and manganese issues. The chapter also describes a methodology for evaluating and selecting the optimum treatment system.

6 Introduction 3 Chapter 5. Oxidation In natural waters, iron and manganese rarely exist in particulate form. Therefore, oxidation is the first step in any treatment system. The selection of the optimum oxidation method(s) is traditionally based on efficiency, chemical and equipment cost, and the chemical characteristics of the source water. This chapter describes when to use which oxidation technologies and offers an overview of the design of the technology. Chapter 6. Clarification For source water with high iron concentrations (above 5 10 mg/l), filtration technologies generally result in a significant amount of backwash water and thus operate at low water efficiency due to short filter run times. In such cases, it may be desirable to provide clarification to remove the bulk of the iron/manganese to improve the filtration process. Clarification has traditionally been limited to sedimentation, and in some instances solids-contact clarification. Over the last two decades, advancements have been made to plate and tube settlers, which has made these high-rate systems viable treatment technologies. In some instances, high-rate technologies such as ballasted flocculation have also been considered. Chapter 6 presents practical design information regarding clarification technologies. Chapter 7. Filtration Filtration has undergone significant advancements in recent years. Historically, filtration was limited to either conventional sand/anthracite or glauconite. Over the past 20 years, however, glauconite supply has become limited and several alternative filtration products have been developed. Chapter 7 describes the design and operating features of the various types of alternate filter media and includes a discussion of biological filtration. Chapter 8. Residuals The iron/manganese treatment process generates residuals that require disposal. Treatment can be provided to reduce the volume of waste and improve the water efficiency of the entire treatment system. Chapter 8 describes residuals treatment options and practical design guidelines.

7 4 Iron and Manganese Removal Handbook Chapter 9. Distribution System Water Quality A significant number of customer complaints are prompted by dirty water, resulting from corrosion in metallic distribution systems and changes in treatment plant practices, such as lowering the chlorine residual on top of the filters to reduce the amount of disinfection by-products. This chapter presents an overview of distribution system water quality as it relates to iron and manganese and provides potential sampling/data collection and remediation options should a system exhibit elevated iron and manganese. Chapter 10. Case Studies These case studies present solutions to a variety of challenges in the field of iron and manganese removal. They include several design examples intended to demonstrate different treatment system designs. Appendices Appendix A details the results of pilot studies conducted on iron and manganese removal processes. Appendix B provides conversion tables and calculation tools for dosing and analyses.